1. Field of the invention
This invention relates to an apparatus for separating non-magnetic materials of different densities according to a difference in density of materials with the aid of a magnetic fluid.
2. Description of the prior art
Magnetic fluids are very stable suspensions of single domain magnetic particles. The suspended particles are so small (typically less than 150A.degree.) that they do not settle under gravity or interact even in the presence of a strong magnetic field. The magnetic response of a magnetic fluid results from the coupling of individual particles with a substantial volume of the bulk liquid. This coupling is facilitated by a stabilizing agent which absorbs on the particle surface and is also solvated by the surrounding liquid.
A magnetic fluid placed in a non-homogeneous magnetic field experiences a net magnetic force which tends to drive it, like all magnetizable objects, towards regions of the highest magnetic intensity.
When a non-magnetic object is immersed in a magnetic fluid in the presence of a magnetic field gradient, there acts a magnetic force on the object, which tends to expel the object to a region of a minimum field.
Description will now be given of a prior art separating apparatus utilizing a difference in density for separating non-magnetic materials, in conjunction with FIGS. 1 and 2.
A magnet 1 produces a given magnetic field having a uniform gradient in a vertical direction in an air gap defined between pole pieces 2 thereof. Disposed within the air gap in the magnet 1 is a non-magnetic trough 3 extending at a right angle to the direction of the magnetic field produced by the magnet 1 but outwardly to both sides of the pole pieces 2. A magnetic fluid 4 is retained in a magnetic field in such a portion of the trough 3, which a magnetic field produced by a magnet 1 penetrates. This magnetic fluid forms a material-separating portion. The magnet 1 is energized by a coil 5. Materials 6 to be separated, which are made up of non-magnetic materials having varying densities, are supplied from a hopper 7 positioned on the lefthand top of the trough 3 into the trough 3, and then transported by means of a transporting conveyor 8 into the central portion of the magnetic fluid 4. Materials 6' having a density lower than an apparent density of the magnetic fluid 4 and contained in the materials 6, which have been charged into the magnetic fluid 4 for separation, float through the magnetic fluid 4 and are transferred by means of a conveyor 10 having material-raking flights 9 thereon and running through an upper portion of the trough 3, then discharged from the righthand end of the trough 3 outside to be recovered in a container 11. On the other hand, materials 6" having a high density sink through the magnetic fluid 4 and are transfered by means of a conveyor 12 positioned in the lower portion of the trough 3 and then taken from the lower lefthand end of the trough 3 outside to be recovered in a container 13.
With this apparatus, the height of a magnetic fluid serving as a material-separating portion should be increased. However, an increase in height of the magnetic fluid 4 tends to result in a lack of uniformity in apparent density of the magnetic fluid 4. In case the amount of materials to be separated is desired to be increased, then the dimensions of an air gap between the pole pieces 2 should be increased. This results in an extreme increase in size of a magnetic field generating means, and hence is not economical.